Cycles: add Path Guiding on CPU through Intel OpenPGL

This adds path guiding features into Cycles by integrating Intel's Open Path
Guiding Library. It can be enabled in the Sampling > Path Guiding panel in the
render properties.

This feature helps reduce noise in scenes where finding a path to light is
difficult for regular path tracing.

The current implementation supports guiding directional sampling decisions on
surfaces, when the material contains a least one diffuse component, and in
volumes with isotropic and anisotropic Henyey-Greenstein phase functions.

On surfaces, the guided sampling decision is proportional to the product of
the incident radiance and the normal-oriented cosine lobe and in volumes it
is proportional to the product of the incident radiance and the phase function.

The incident radiance field of a scene is learned and updated during rendering
after each per-frame rendering iteration/progression.

At the moment, path guiding is only supported by the CPU backend. Support for
GPU backends will be added in future versions of OpenPGL.

Ref T92571

Differential Revision: https://developer.blender.org/D15286

1 files changed, 1 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ef3309ded48..d8adf6c396f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -429,6 +429,7 @@ mark_as_advanced(WITH_CPU_SIMD)
 # Cycles
 option(WITH_CYCLES                   "Enable Cycles Render Engine" ON)
 option(WITH_CYCLES_OSL               "Build Cycles with OpenShadingLanguage support" ON)
+option(WITH_CYCLES_PATH_GUIDING      "Build Cycles with path guiding support" ON)
 option(WITH_CYCLES_EMBREE            "Build Cycles with Embree support" ON)
 option(WITH_CYCLES_LOGGING           "Build Cycles with logging support" ON)
 option(WITH_CYCLES_DEBUG             "Build Cycles with options useful for debugging (e.g., MIS)" OFF)